Crown compounds have found extensive applications such as phase transfer catalysts for organic syntheses, selective capture and separation of metal ions, resolution of optical isomers of amino acids, uses in ion selective electrodes, and uses in pharmaceuticals, agricultural chemicals, photographic emulsions, etc.
To facilitate the use of crown compounds in these areas, it is desired that highly purified crown compounds be able to be obtained more easily at cheaper prices.
As processes for synthesizing crown compounds, those described in J. Am. Chem. Soc. Vol. 89, p. 7017 (1967), for example, are known; however, there are no description on any purification process capable of providing a crown compound of adequate purity. Organic Syntheses, vol. 52, p. 66 (1972) describes a process for recrystallizing crown compounds from benzene or dioxane, but the process shown therein has disadvantages such as inabilities of providing an adequate purity or a high yield, use of toxic solvents, high costs, etc.
Further, crown compounds include those which are liquid at ordinary temperature and can be hardly purified by recrystallization, an example of which is 15-crown-5. Crown compounds are relatively stable to heat and may be purified by distillation; but, distillation of ethers such as crown compounds on an industrial scale is not favorable because ethers are liable to yield explosive peroxides when contacted with air at high temperature.
As described above, there has not been found so far any process capable of purifying safely and efficiently crown compounds which are liquid at ordinary temperature; therefore, development of such a process is desired.